Microbial organisms, mice, rats, guinea pigs, and rabbits have been exposed to intense fields of 2450-MHz microwave energy in the multi-mode cavity in studies of ultrastructural, teratological, thermal, behavioral, and growth responses to radiation. At rates of dosing exceeding 40 mW/g and durations of radiation of many hours, there are reliable differences in parameters of growth and in ultrastructure of microbial (bacterial and fungal) organisms as compared to conventionally thermalized controls. At rates of dosing below 40 mW/g and durations less than 25 min, radiated mammals seldom differed reliably from non-radiated controls except for the observation that fetal radiation improved survival of mice treated in utero with a teratogenic agent.